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.Dd $Mdocdate: April 25 2020 $
.Dt SSL_CTX_SET_CIPHER_LIST 3
.Os
.Sh NAME
.Nm SSL_CTX_set_cipher_list ,
.Nm SSL_set_cipher_list
.Nd choose list of available SSL_CIPHERs
.Sh SYNOPSIS
.In openssl/ssl.h
.Ft int
.Fn SSL_CTX_set_cipher_list "SSL_CTX *ctx" "const char *control"
.Ft int
.Fn SSL_set_cipher_list "SSL *ssl" "const char *control"
.Sh DESCRIPTION
.Fn SSL_CTX_set_cipher_list
sets the list of available cipher suites for
.Fa ctx
using the
.Fa control
string.
The list of cipher suites is inherited by all
.Fa ssl
objects created from
.Fa ctx .
.Pp
.Fn SSL_set_cipher_list
sets the list of cipher suites only for
.Fa ssl .
.Pp
The control string consists of one or more control words
separated by colon characters
.Pq Ql \&: .
Space
.Pq Ql \ \& ,
semicolon
.Pq Ql \&; ,
and comma
.Pq Ql \&,
characters can also be used as separators.
Each control words selects a set of cipher suites
and can take one of the following optional prefix characters:
.Bl -tag -width Ds
.It \&No prefix:
Those of the selected cipher suites that have not been made available
yet are added to the end of the list of available cipher suites,
preserving their order.
.It Prefixed minus sign Pq Ql \- :
Those of the selected cipher suites that have been made available
earlier are moved back from the list of available cipher suites to
the beginning of the list of unavailable cipher suites,
also preserving their order.
.It Prefixed plus sign Pq Ql + :
Those of the selected cipher suites have been made available earlier
are moved to end of the list of available cipher suites, reducing
their priority, but preserving the order among themselves.
.It Prefixed exclamation mark Pq Ql \&! :
The selected cipher suites are permanently deleted, no matter whether
they had earlier been made available or not, and can no longer
be added or re-added by later words.
.El
.Pp
The following special words can only be used without a prefix:
.Bl -tag -width Ds
.It Cm DEFAULT
An alias for
.Sm off
.Cm ALL No :! Cm aNULL No :! Cm eNULL .
.Sm on
It can only be used as the first word.
The
.Cm DEFAULT
cipher list can be displayed with the
.Xr openssl 1
.Cm ciphers
command.
.It Cm @STRENGTH
Sort the list by decreasing encryption strength,
preserving the order of cipher suites that have the same strength.
It is usually given as the last word.
.El
.Pp
The following words can be used to select groups of cipher suites,
with or without a prefix character.
If two or more of these words are joined with plus signs
.Pq Ql +
to form a longer word, only the intersection of the specified sets
is selected.
.Bl -tag -width Ds
.It Cm ADH
Cipher suites using ephemeral DH for key exchange
without doing any server authentication.
Equivalent to
.Cm DH Ns + Ns Cm aNULL .
.It Cm AEAD
Cipher suites using Authenticated Encryption with Additional Data.
.It Cm AECDH
Cipher suites using ephemeral ECDH for key exchange
without doing any server authentication.
Equivalent to
.Cm ECDH Ns + Ns Cm aNULL .
.It Cm aECDSA
Cipher suites using ECDSA server authentication.
.It Cm AES
Cipher suites using AES or AESGCM for symmetric encryption.
.It Cm AES128
Cipher suites using AES(128) or AESGCM(128) for symmetric encryption.
.It Cm AES256
Cipher suites using AES(256) or AESGCM(256) for symmetric encryption.
.It Cm AESGCM
Cipher suites using AESGCM for symmetric encryption.
.It Cm aGOST
An alias for
.Cm aGOST01 .
.It Cm aGOST01
Cipher suites using GOST R 34.10-2001 server authentication.
.It Cm ALL
All cipher suites except those selected by
.Cm eNULL .
.It Cm aNULL
Cipher suites that don't do any server authentication.
Not enabled by
.Cm DEFAULT .
Beware of man-in-the-middle attacks.
.It Cm aRSA
Cipher suites using RSA server authentication.
.It Cm CAMELLIA
Cipher suites using Camellia for symmetric encryption.
.It Cm CAMELLIA128
Cipher suites using Camellia(128) for symmetric encryption.
.It Cm CAMELLIA256
Cipher suites using Camellia(256) for symmetric encryption.
.It Cm CHACHA20
Cipher suites using ChaCha20-Poly1305 for symmetric encryption.
.It Cm COMPLEMENTOFALL
Cipher suites that are not included in
.Cm ALL .
Currently an alias for
.Cm eNULL .
.It Cm COMPLEMENTOFDEFAULT
Cipher suites that are included in
.Cm ALL ,
but not included in
.Cm DEFAULT .
Currently similar to
.Cm aNULL Ns :! Ns Cm eNULL
except for the order of the cipher suites which are
.Em not
selected.
.It Cm 3DES
Cipher suites using triple DES for symmetric encryption.
.It Cm DH
Cipher suites using ephemeral DH for key exchange.
.It Cm DHE
Cipher suites using ephemeral DH for key exchange,
but excluding those that don't do any server authentication.
Similar to
.Cm DH Ns :! Ns Cm aNULL
except for the order of the cipher suites which are
.Em not
selected.
.It Cm ECDH
Cipher suites using ephemeral ECDH for key exchange.
.It Cm ECDHE
Cipher suites using ephemeral ECDH for key exchange,
but excluding those that don't do any server authentication.
Similar to
.Cm ECDH Ns :! Ns Cm aNULL
except for the order of the cipher suites which are
.Em not
selected.
.It Cm ECDSA
An alias for
.Cm aECDSA .
.It Cm eNULL
Cipher suites that do not use any encryption.
Not enabled by
.Cm DEFAULT ,
and not even included in
.Cm ALL .
.It Cm GOST89MAC
Cipher suites using GOST 28147-89 for message authentication
instead of HMAC.
.It Cm GOST94
Cipher suites using HMAC based on GOST R 34.11-94
for message authentication.
.It Cm HIGH
Cipher suites of high strength.
.It Cm kGOST
Cipher suites using VKO 34.10 key exchange, specified in RFC 4357.
.It Cm kRSA
Cipher suites using RSA key exchange.
.It Cm LOW
Cipher suites of low strength.
.It Cm MD5
Cipher suites using MD5 for message authentication.
.It Cm MEDIUM
Cipher suites of medium strength.
.It Cm NULL
An alias for
.Cm eNULL .
.It Cm RC4
Cipher suites using RC4 for symmetric encryption.
.It Cm RSA
Cipher suites using RSA for both key exchange and server authentication.
Equivalent to
.Cm kRSA Ns + Ns Cm aRSA .
.It Cm SHA
An alias for
.Cm SHA1 .
.It Cm SHA1
Cipher suites using SHA1 for message authentication.
.It Cm SHA256
Cipher suites using SHA256 for message authentication.
.It Cm SHA384
Cipher suites using SHA384 for message authentication.
.It Cm SSLv3
An alias for
.Cm TLSv1 .
.It Cm STREEBOG256
Cipher suites using STREEBOG256 for message authentication.
.It Cm TLSv1
Cipher suites usable with the TLSv1.0, TLSv1.1, and TLSv1.2 protocols.
.It Cm TLSv1.2
Cipher suites for the TLSv1.2 protocol.
.It Cm TLSv1.3
Cipher suites for the TLSv1.3 protocol.
If the
.Fa control
string selects at least one cipher suite but neither contains the word
.Cm TLSv1.3
nor specifically includes nor excludes any TLSv1.3 cipher suites, all the
.Cm TLSv1.3
cipher suites are made available, too.
.El
.Pp
The full words returned by the
.Xr openssl 1
.Cm ciphers
command can be used to select individual cipher suites.
.Pp
The following words do not match anything because
LibreSSL no longer provides any such cipher suites:
.Pp
.Bl -tag -width Ds -compact
.It Cm DES
Cipher suites using single DES for symmetric encryption.
.It Cm DSS
Cipher suites using DSS server authentication.
.It Cm IDEA
Cipher suites using IDEA for symmetric encryption.
.El
.Pp
The following are deprecated aliases:
.Pp
.Bl -column kEECDH ECDHE -compact -offset indent
.It    avoid: Ta    use:
.It Cm EDH    Ta Cm DHE
.It Cm EECDH  Ta Cm ECDHE
.It Cm kEDH   Ta Cm DH
.It Cm kEECDH Ta Cm ECDH
.El
.Pp
Unknown words are silently ignored, selecting no cipher suites.
Failure is only flagged if the
.Fa control
string contains invalid bytes
or if no matching cipher suites are available at all.
.Pp
On the client side, including a cipher suite into the list of
available cipher suites is sufficient for using it.
On the server side, all cipher suites have additional requirements.
ADH ciphers don't need a certificate, but DH-parameters must have been set.
All other cipher suites need a corresponding certificate and key.
.Pp
A RSA cipher can only be chosen when an RSA certificate is available.
RSA ciphers using DHE need a certificate and key and additional DH-parameters
(see
.Xr SSL_CTX_set_tmp_dh_callback 3 ) .
.Pp
A DSA cipher can only be chosen when a DSA certificate is available.
DSA ciphers always use DH key exchange and therefore need DH-parameters (see
.Xr SSL_CTX_set_tmp_dh_callback 3 ) .
.Pp
When these conditions are not met
for any cipher suite in the list (for example, a
client only supports export RSA ciphers with an asymmetric key length of 512
bits and the server is not configured to use temporary RSA keys), the
.Dq no shared cipher
.Pq Dv SSL_R_NO_SHARED_CIPHER
error is generated and the handshake will fail.
.Sh RETURN VALUES
.Fn SSL_CTX_set_cipher_list
and
.Fn SSL_set_cipher_list
return 1 if any cipher suite could be selected and 0 on complete failure.
.Sh SEE ALSO
.Xr ssl 3 ,
.Xr SSL_CTX_set1_groups 3 ,
.Xr SSL_CTX_set_tmp_dh_callback 3 ,
.Xr SSL_CTX_use_certificate 3 ,
.Xr SSL_get_ciphers 3
.Sh HISTORY
.Fn SSL_CTX_set_cipher_list
and
.Fn SSL_set_cipher_list
first appeared in SSLeay 0.5.2 and have been available since
.Ox 2.4 .
.Sh CAVEATS
In LibreSSL,
.Fn SSL_CTX_set_cipher_list
and
.Fn SSL_set_cipher_list
can be used to configure the list of available cipher suites for
all versions of the TLS protocol, whereas in OpenSSL, they only
control cipher suites for protocols up to TLSv1.2.
If compatibility with OpenSSL is required, the list of
available TLSv1.3 cipher suites can only be changed with
.Fn SSL_set_ciphersuites .
